The present invention relates to a registration fixture for holding, aligning, heating and registering the plates of a dual diaphragm pressure capsule during a vacuum-temperature-pressure sealing process.
The incorporation of pressure sensors into the electronic control systems of automotive vehicles poses severe operational requirements for the pressure sensor. These requirements are further heightened when the pressure sensor is used to measure the manifold pressure (MP) or the absolute manifold pressure (MAP) of the engine.
The pressure sensor must operate in a mobile and severely hostile environment which may include any of the following characteristics: varied temperature extremes, excessive shock and vibration and high levels of electromagnetic interference and corrosive gases and liquids. The pressure proximate the intake manifold is rapidly changeable and susceptable to large variations in magnitude (1-4 atmospheres) which may be caused as the result of explosive backfire or may occur during the boost phase of the operation of a supercharger or turbocharger; thus requiring a pressure sensor having a large dynamic range and high sensitivity. Irrespective of the above, if the present invention is utilized in an automobile, the requirements of the industry dictate that it must be (1) inexpensive, (2) repeatable, and (3) capable of being mass produced which implicitly requires the use of novel and rapid cost effective fabrication techniques as opposed to the slower ion-milling vacuum deposition methods such as sputter-etching techniques or brazing techniques as mentioned by Polye in U.S. Pat. No. 3,858,097 and by Dias, et al in U.S. Pat. No. 4,064,550.
The present invention is a registration fixture for holding both plates of a quartz capacitance pressure capsule in aligned relationship during the sealing of both plates together.
The fixture comprises a plurality of flat metallic plates. Each metallic plate has at least one pressure capsule receiving cavity to receive one of the quartz plates of the pressure capsule. In addition, the fixture includes means for aligning each metallic plate and hence, each quartz plate at a determinable orientation to each other. The preferred embodiment of the fixture illustrates a fixture for aligning, registering and holding in a stacked relationship, a plurality of the pressure capsules to be assembled.
Each metal plate partially envelopes its corresponding quartz plate. In this manner, the fixture provides a means for uniformly irradiating each quartz plate during the described temperature-pressure sealing process. The registration fixture described in the preferred embodiment is fabricated of steel alloy (RA 330) however, other metals and ceramics may be substituted. In addition, the optimum pressure capsule yield appears to occur when each member of the registration fixture has an oxide coating. This coating is achieved by baking or otherwise heat treating each metallic plate.
It is an object of the present invention to provide a registration fixture to hold a plurality of pressure capsules in stacked separated engagement.